Project Summary/Abstract This revised K23 Mentored Career Development Award will support the candidate in developing an independent research career to investigate determinants of children?s mental health services use in usual care settings and the long-term preventive effects of children?s mental health services use on adolescent behavioral outcomes including psychosocial functioning and substance use. This award will provide the candidate with extensive training in substance use epidemiology, health policy, health services research, advanced longitudinal data analysis and latent variable analysis, and mixed-methods research. This training will permit the candidate to expand understanding of how evidence-based mental health services impact later substance use, an important public health outcome, and inform more individualized targeted mental health services and substance use prevention. This K23 Award will provide the candidate the methodological and analytical skills needed to reach a long-term career goal of developing and implementing a patient-centered research program focused on improving youths? substance use outcomes and access to quality care. Randomized controlled trial follow-up studies suggest that treatment for childhood mental disorders (CMD) reduces risk of substance use; however, these studies cannot elucidate how patterns of children?s use of mental health services in the community affect later substance use. Further, research identifying moderators and mediators of the association between treatment for childhood mental illness and later substance use is lacking. Thus, the proposed research project will examine treatment patterns for primary CMD, associated substance use outcomes in adolescence, and potential mediating and moderating factors of the association. Additionally, a mixed methods approach, including focus group data from key stakeholders (adolescents, their parents, and mental health care providers), will further elucidate barriers and facilitators to evidence-based mental health services and other treatment challenges. Specific aims include: 1) Characterize children?s patterns of mental health service use in usual care settings; identify demographic and clinical factors associated with continuity of service use and receipt of guideline concordant care; 2) Determine the effects of usual care on proximal risk factors for SUD and subsequent problematic substance use; assess whether proximal risk factors mediate the effect of usual care for CMD on problematic substance use in adolescence. 3) Assess whether early SUD risk factors moderate the effect of usual care for CMD on problematic substance use in adolescence. 4) Assess the reciprocal effects of substance use/SUD and CMD over the course of child and adolescent development. 5) Conduct focus groups with key stakeholders to gain a deeper understanding of barriers to guideline-concordant care and aid in developing strategies to optimize access to quality care and decrease substance use risk among vulnerable youth. This project?s innovative focus on examining long-term public health impacts of children?s mental health services within the developmental context, analysis of longitudinal data from an at-risk sample, and use of mixed methods will contribute to understanding of adolescent SUD risk and protective factors and barriers and facilitators of evidence-based services.